1. Field of the Invention
The present invention relates to a torque control apparatus and a vehicle control system having the same.
2. Description of Related Art
In a previously proposed control system of an internal combustion engine of a vehicle, a torque demand (also referred to as a demanded torque) is computed based on an operational amount (an accelerator operational amount or alternatively referred to as an opening degree) of an accelerator operated by a driver, and then actuators of the engine are operated to achieve this torque demand. For example, according to Japanese Unexamined Patent Publication No. 11-50889, a target shaft torque of an engine is computed based on an accelerator operational amount and an engine rotational speed, and a combustion pressure torque is computed based on the target shaft torque and an engine operational state. Then, a target intake air quantity is computed based on the combustion pressure torque, and an opening degree of a throttle valve is controlled in a manner that achieves the target intake air quantity. Furthermore, at the time of computing the combustion pressure torque, a frictional torque loss, a pump torque loss and an indicated torque are computed based on the engine operational state (e.g., an engine rotational speed, an engine coolant temperature, an engine load), and the combustion pressure torque is computed based on them.
However, the combustion state of the engine changes with time. Therefore, for example, a cylinder temperature and a cylinder pressure change due to the change in the combustion state. Accordingly, the torque loss also changes. For example, a torque loss in a fuel cut-off period differs from a torque loss in a normal combustion period. In such a case, the torque loss cannot be accurately computed, and thereby a torque demand, which is demanded by a driver, cannot be achieved.
Lately, development of a torque based control system is in progress for implementing its commercial use. The torque based control system collectively controls operation of various actuators in addition to the engine based on the torque demand, which is demanded by a driver. In this torque based control system, when the torque demand cannot be met in the engine, a torque balance relative to the other actuators is deteriorated, so that the desired vehicle control cannot be implemented. For example, in a case of a brake control apparatus, which controls braking of the vehicle, at the time of decelerating the vehicle, the torque demand may be met by a brake system. However, at this time, in the engine side, fuel cut-off is executed, and thereby an error in an engine torque occurs due to a change in a torque loss caused by the fuel cut-off. Therefore, in such a case, a demanded deceleration may not be achieved.